1. Field of the Invention
The present invention relates to a stacked memory in which a plurality of semiconductor devices are stacked and a manufacturing method thereof. In particular, the present invention relates to a stacked memory used in a harsh environment and a manufacturing method thereof.
2. Description of the Related Art
A stacked memory is composed of a plurality of stacked semiconductor devices, each of which is packaged in a CSP (Chip Size Package), a TSOP (Thin Small Outline Package), or the like. The stacked memory is mounted on a motherboard together with other electronic components to compose a semiconductor memory device or the like. The semiconductor memory device in which the stacked memory is installed, for example, does not need a mechanical drive section and rotation section, which are necessary in a magnetic tape recorder and a hard disk, and operates at high speed with low power consumption. Thus, it is considered that the semiconductor memory device with the stacked memory is applied to a device for temporarily storing satellite data, that is, a data recorder.
FIGS. 1 and 2 are perspective views showing conventional stacked memory. In a stacked memory 20, as shown in FIG. 1, for example, leads 21 of the CSPs, TSOPs, or the like are connected to a carrier substrate by soldering or the like to achieve multilayer packaging (refer to, for example, Japanese Patent Laid-Open Publication No. 135716/1999 and No. 031617/2000). As a stacked memory 30 shown in FIG. 2, another configuration has been practically used in which after a plurality of semiconductor devices are fixed by a mold material, lead surfaces are exposed by cutting, and then wiring is formed by a metallization method, a laser cut method or the like (refer to, for example, Japanese Patent Laid-Open Publication No. 286380/2000).
The foregoing conventional techniques, however, have the following problems. A semiconductor memory device used in artificial satellite equipment is exposed to a harsh environmental condition, for example, used in vacuum, under a large temperature variation, large vibration, and the like, so that high heat radiation and high resistance to vibration are required of the stacked memory mounted on the semiconductor memory like this.
In said stacked memory 20 shown in FIG. 1, a plurality of semiconductor devices are mounted in a stacked fashion by solder joints, and metal leads 21 are extended to a top face of the CSP or the TSOP in consideration of heat radiation. However, heat radiation from the TSOPs disposed in the middle layers is not considered. Since soldering is also used in joining metal leads 21 of the stacked memory 20, there are cases where solder in lead joints remelts when the stacked memory 20 is mounted on the motherboard. Thus, after the stacked memory is mounted on the motherboard, it is necessary to reconfirm portions, which have been joined by soldering before mounting. In equipment requiring high reliability such as equipment installed in an artificial satellite and the like, all solder joints are visually confirmed. In a case that the solder joints remelt, the solder joints have to be visually reconfirmed, and hence there is a problem that time involved in a manufacturing process and manufacturing is increased.
Furthermore, in said stacked memory 30 having structure shown in FIG. 2, semiconductor device packages such as the CSPs, TSOPs, and the like are just fixed by a mold material. Accordingly, there is a problem that positive measures against heat radiation with the use of a high heat conductive material such as metal and the like are not taken.